1. Field of the Invention
This invention is directed to acousto-optic filtering devices, in general, and to an improved acousto-optic device which permits relatively high frequency signals to be detected with presently available technology, in particular.
2. Prior Art
There are many known acousto-optic detectors available in the technology today. These detectors are used to detect electrical signals, to convert the signals to optical signals and to then reconvert the optical signals to electrical signals. These devices provide a detecting scheme without requiring a direct interfacing with the signal source or direct reading of the electrical signals.
In many cases, the existing acousto-optical detection apparatus includes a Bragg cell therein. The Bragg cell permits the detection apparatus to be controlled in several respects. For example, by controlling the operation of the Bragg cell, a carefully controlled diffraction grating effect can be obtained. This then permits the output signal to be controlled and/or defined in a fairly rigorous manner.
However, most of the prior art detectors of this nature use photo-detector cells and/or arrays in the conversion from optical to electrical signals. While this is not a disadvantage, per se, it is a limiting factor in that most photodetector cells or arrays are relatively slow operating devices. That is, most of the existing photo-detector cells or arrays are fabricated of silicon based materials (in solid state applications) or photo-multiplier tubes. Typically, these types of detectors can operate only in the low hundreds of megahertz range. Conversely, in many of the applications for this type of signal detection, the signals provided are in the multi-gigahertz range. Because of the two to three orders of magnitude difference in signal frequency, the existing photodetectors are not satisfactory for use with high frequency acousto-optical detector systems. Consequently, the existing acousto-optical systems cannot be used in the high frequency ranges.